The Anatomy of the Abdominal Aorta

The end of the largest blood vessel in the body

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The aorta is the largest blood vessel in the body. It is an artery, meaning that it carries blood away from the heart. The abdominal aorta enters the abdomen through the diaphragm at the level of the twelfth thoracic vertebre and continues to just below the umbilical area, where it splits into the right and left common iliac arteries. The aorta supplies oxygenated blood to most of the body.

Since so much blood flows through the aorta, it is an extremely sensitive blood vessel during trauma or certain types of medical conditions. If it is cut or ruptured, the aorta can lose the majority of the body's total blood volume in a few minutes, which can lead to death.

The aorta starts at the left ventricle of the heart and curves around toward the feet. The curve is known as the aortic arch. The entire aorta stretches from the thoracic cavity to the abdomen. All of the blood flow leaving the left ventricle flows through some or all of the aorta.

The area just above where the abdominal aorta bifurcates (divides into two branches) into the iliac arteries is susceptible to a weakening of the aortic wall called an abdominal aortic aneurysm. If diagnosed before a rupture occurs, an abdominal aortic aneurysm can be surgically repaired.

Anatomy

Inferior to the diaphragm begins the abdominal aorta. It descends from the location of the diaphragm, at about the twelfth thoracic vertebra, down to where it bifurcates into the left and right common iliac arteries.

Structure of the Abdominal Aorta

The aorta is the largest blood vessel in the body by width and also as measured by total blood volume transported. Like other arteries, it consists of a thick wall with the ability to constrict and relax as needed to adjust for low and high blood pressures. The wall has three main layers:

  1. Tunica intima (tunica interna) is the innermost layer, and it is a simple squamous epithelium-lined with an elastic basement membrane that provides a smooth surface for blood to flow.
  2. Tunica media is the next, thick layer of smooth muscle that provides strength and the ability for the aorta to dilate or contract as necessary.
  3. Tunica adventitia (tunica externa) is the outermost layer of the aorta and connects it to surrounding tissues and structures within the body.

Location of the Abdominal Aorta

The abdominal aorta lines up just to the left of midline in the abdominal cavity. It averages approximately 13 centimeters from the diaphragm to its bifurcation. In that short distance, the abdominal aorta gives rise to several major arteries:

  • Phrenic artery
  • Celiac trunk
  • Suprarenal arteries
  • Superior mesenteric artery
  • Renal arteries
  • Gonadal arteries
  • Inferior mesenteric artery

Abdominal aorta diameter is typically between 29.9 and 33.2 millimeters depending on age, based on a study measuring males from 30 to 79 years old.

The abdominal aorta gets wider as we get older and it gets less flexible.

In the same study, younger men's abdominal aorta stretched an average of 9 percent, while their elder counterparts only stretched 5 percent when the heart was pushing blood (systole).

Anatomical Variations of the Abdominal Aorta

Congenital abdominal aortic aneurysm (AAA) is a very rare condition that affects mostly kids under the age of three years old, but can also be found in fetuses and in young adults. In extremely rare cases, fistulas can form between the abdominal aorta and surrounding structures.

Function

As the largest blood vessel in the body, the aorta provides a conduit for all the blood flowing to the body from the heart other than the blood that flows to the heart itself. The abdominal aorta conducts blood to organs in the abdominal cavity as well as to the legs and feet. Also, the aorta helps to control blood pressure by dilating and constricting as necessary.

Clinical Significance

The most common condition to affect the abdominal aorta is an abdominal aortic aneurysm (AAA). An abdominal aortic aneurysm consists of a weakening of the wall of the aorta just above the point where it bifurcates into the left and right common iliac arteries. An abdominal aortic aneurysm is a fairly common condition that affects men over the age of 60.

While an aneurysm can occur in other parts of the aorta, the abdomen is the area least likely to show significant signs and symptoms.

The abdomen allows a lot of room for a weak aorta to expand and grow. It can develop a "bubble" of sorts, which can be compared visually to a snake that swallowed a rat—sort of bloated in one spot. Signs and symptoms of an abdominal aortic aneurysm are back pain, deep abdominal discomfort, and possibly a pulsating mass in the abdomen.

If a rupture occurs in the inside lining of the aorta, the tunica intima, it can lead to blood being forced between the tunica intima and the tunica media (the inside and middle layers of the aorta). Blood forced between them can lead to a separation of the two layers, known as a dissection. Dissections can also happen in the other parts of the aorta that live in the thoracic cavity (the chest), but abdominal aortic aneurysms are the most common.

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